The present invention relates to glare reduction in transparent substrates, particularly glass. Low gloss, glare reducing glass is utilized in a wide array of applications such as cathode ray tube screens or other display devices (monitors, televisions, liquid crystal displays, etc.); input or selection devices such as touch screens or input panels; glass enclosed displays (museums or other public displays); optical filters; picture frames; windows for architectural applications; glass components employed in mirrors; solar collector cover plates; optical lenses utilized in eyewear and viewing devices; and windshields for vehicles.
There are primarily two methods of reducing glare associated with surfaces of glass substrates. The first method involves depositing an "interference" coating stack on the glass substrate that controls glare by taking advantage of the optical interference within thin films. Such films usually have a thickness of about one-quarter or one-half the nominal wavelength of visible light, depending on the relative indexes of refraction of the coating and glass. The second method involves forming a light scattering, i.e. diffusing, means at the surface of the glass, usually by altering the characteristics of the outermost surface of either the glass substrate or via a diffuser coating on the glass substrate.
Interference coatings reduce glare without reducing resolution. However, they are relatively expensive to deposit, requiring the use of relatively high cost vacuum deposition techniques such as sputtering and precise manufacturing conditions, or very precise alkoxide solution dip coating techniques, with subsequent drying and firing. Strict thickness control and uniformity are required.
In attempting to reduce glare by diffusion of light (the second method noted above), prior artisans have etched the outer surface of the glass substrate, or etched or otherwise modified the outer surface of a coating deposited on the glass substrate. There are numerous drawbacks in etching or otherwise modifying the surface characteristics of a substrate or coated substrate. Etching by chemical means involves handling and storage of generally highly corrosive compounds (e.g. hydrofluoric acid). Such compounds create processing and disposal problems in view of increasingly stringent environmental laws. Etching by non-chemical means, such as by sandblasting, necessitates additional and costly processing operations.
As an alternative to etching or altering the surface characteristics of a substrate or coated substrate, prior artisans formed relatively thick coatings, e.g. 10-20 microns, with particular surface characteristics on the substrates in order to reduce glare, and avoid the necessity of etching. This has been done, for example, by incorporating diverse materials into the coating solution which will yield coatings of mixed oxides. Other prior artisans have dispersed fine microparticles such as silica, in a suspension, typically aqueous, and applied the resulting dispersion to a glass surface. When the carrier liquid evaporates, the microparticles cling tenaciously to the glass surface and reduce gloss therefrom.
However, when attempting to reduce glare with a diffuser means, either by etching or by depositing a coating having particular surface characteristics to reduce glare, there can be a significant loss in resolution of images viewed through the substrate. That is, as the glare reducing ability of the glass substrate or coated glass substrate increases, the resolution of images viewed through the substrate decreases. Thus, there is a need for a diffusing method of reducing gloss which does not significantly reduce the resolution of images viewed through the substrate. In addition, there is a need for reduced gloss, high resolution coatings that may be deposited or formed on substrates.